How do Archaeologists Excavate Sites?
Archaeological sites are fragile, non-renewable resources. Once a site is excavated, it is gone forever. The artifacts and soil cannot be put back in place and the site reconstructed. Archaeologists only excavate sites when they are threatened by destruction or when they can reveal important information that cannot be found any other way. Archaeologists prefer to preserve our finite resources rather than dig them up for no purpose. The five large excavation projects undertaken at Fort Bragg were done because each site was in jeopardy of being destroyed. The archaeological work recovered the important information that might be lost. Here are the basic steps to conducting scientific archaeological excavations.
Step One: Make a Plan
Archaeologists must have a clear reason and plan, called a research design, for excavating a site before they put a shovel in the ground. They must be able to answer these questions:
- Why are we excavating the site?
- What questions do we want to answer?
- How will we conduct the excavations?
- How will we analyze the artifacts?
- Do I have enough time and money to write a report?
Step Two: Setting out a Grid
Archaeologists begin all excavations by creating a measured grid across the area that will be studied. The grid helps them keep track of where they dig test units and where they find artifacts. Every artifact and feature on an archaeological site has a precise horizontal (side to side) and vertical (up and down ) location that is recorded. This is called context. It is the spatial relationship of artifacts and features to each other that provides archaeologists with important information about the past.
Artifacts are objects made and/or used by people.
Features are non-portable elements such as soil stains, architectural remnants, storage pits, and garbage dumps.
Ecofacts are plant and animal remnants that help archaeologists understand the natural resources people ate, made clothes with, or used to build their homes.
Step Three: Excavating Units
Archaeologists excavate units to uncover features and to recover artifacts left behind at the site. The north-south and east-west coordinates of each unit are plotted on the site grid. Excavation units usually are one-by-one meter or two-by-two meter squares or one-by-two meter rectangles. Archaeologists use shovels, trowels, spoons, whisk brooms, and dental picks to carefully remove the unit soil. The units are dug in layers, generally about four inches thick. This helps archaeologists keep track of the depth below the ground surface where artifacts and features are located. Excavators sift all of the excavated dirt through ¼-inch wire mesh screen to help them find artifacts. It is easy to miss small artifacts such as buttons, beads, and flakes during regular shoveling.
Sometimes archaeologists use the site’s natural stratigraphy when they dig. Stratigraphy is the layering of one soil deposit upon another. Think of stratigraphy as a cake with multiple layers of cake and filling. Artifacts found in the lowest levels usually are older than ones found in the higher layers. Sometimes we know when artifacts were made, particularly manufactured goods such as dishes, metal buttons, and patented products. Archaeologists can use these artifacts to date the soil layers they see at the site. On precontact sites, archaeologists rely on radiocarbon dates. All living things absorb radioactive carbon until they die. Since radioactive carbon breaks down over time at a known rate, scientists can measure the amount of radioactive carbon in charcoal, bone, or shell to estimate the material’s age.
Step Four: Identifying Artifacts
When excavators find artifacts, they place them in acid free plastic bags labeled with the site number, excavation unit and level number, feature number, date, and the name of the excavator. The artifacts go back to the archaeological laboratory where they are washed, identified, cataloged, and analyzed. Laboratory specialists begin by separating artifacts by material type — stone, bone, shell, pottery, glass, metal, plastic, wood, fabric, etc. Artifacts in each of these groups are separated again by distinguishing characteristics such as color, size, function, and decoration. Objects in each final category are counted, weighed, and measured. Laboratory specialists enter all of this information into a computer database. Archaeologists spend a lot more time in the laboratory identifying and analyzing artifacts than they do excavating a site.
Step Five: What Does It All Mean?
The most important part of archaeological work is the analysis and report writing. Archaeologists analyze the data to try to answer the questions they set out in their research design. They present their ideas and conclusions about the archaeological materials in a report so other researchers and scientists, interested citizens, and descendants who may have ties to the people who once lived or worked at the site can read about their work.